Heterophoria is a latent squint that is only recognizable with one-eyed vision. With binocular vision, the latent visual defect is involuntarily compensated for by the motor and sensory alignment of the two eyes via active muscle power. If binocular vision is interrupted and the line of sight of both eyes can no longer be coordinated, most people experience a slight divergence in the visual axes of the two eyes.
What is heterophoria?
When both eyes are aligned to a point in the distance, our motor and sensory adjustment mechanisms in both eyes ensure an exactly parallel alignment of the two visual axes via the outer eye muscles.
Otherwise, without these adjustment mechanisms, the image would be blurred or even double imaged. When the far point comes towards us and we continue to fixate on it with both eyes, both visual axes are gradually actively rotated inwards by a few arc seconds, and at extreme closeness by several degrees.
If there is no active alignment of the visual axis when fixing a point in the distance and thus also the motor adjustment mechanism of the eyes, about 80 percent of people experience a slight twisting of the visual axis of the non-active eye. De facto, this constitutes a slight squint.
The deviation of the visual axis of the inactive eye can be rotated slightly inwards, outwards or upwards or downwards around all three spatial axes. Combinations of misaligned or decoupled viewing axes between inside/outside and top/bottom are also possible. As a rule, the heterophoria is only a few seconds of arc to a few degrees by which the visual axes deviate from parallelism.
Three possible causal complexes are held responsible as triggers and causes of heterophoria, after which latent squinting is named and classified. A distinction is made between static, accommodative and neurogenic heterophoria. All anatomical components such as the eye socket (orbita) and the position and nature of the holding apparatus of the eyeball are included in the static cause complex.
Accommodative heterophorias can be caused by refractive errors or by a certain form of farsightedness. Neurogenic factors for the development of heterophoria can consist of problems in the nervous transmission of visual impulses.
A disturbed further processing of the signals in the ganglia or in the CNS can also be a cause. This results in limited or completely failed “image processing”. Decreased neurological processing of the neuronal impulses usually also leads to the inability of the sensory image fusion of both eyes.
Symptoms, Ailments & Signs
In the vast majority of cases, heterophoria is only weakly pronounced. Errors in the non-parallelism of the two visual axes during distance accommodation are corrected without symptoms by the motor-sensory adjustment mechanism in binocular vision. Only in the case of more pronounced heterophoria is the external eye musculature so strained by the active adjustment mechanism that non-specific symptoms appear.
Some of the observed symptoms and signs can exist, for example, in the form of headaches and blurred vision because the unconscious control mechanism of the outer eye muscles is overwhelmed. With even more pronounced heterophoria, dizziness, lack of concentration and increased sensitivity to glare can also occur.
Typically, the signs and symptoms summarized under the term asthenopia do not appear until later in the day. This is most likely related to gradual fatigue of the outer eye muscles.
Diagnosis & disease progression
Normally, in which no symptoms of heterophoria occur, this type of ametropia remains undetected and has no consequences. It is only advisable to carry out an examination and clarification in this regard if the symptoms show increasing symptoms over the course of the day. Devices commonly used to examine any type of squint (strabismus) and to clarify the differential diagnosis are optotype projectors, haploscopes and the much more complex phase difference haploscope.
The latent ametropia of a heterophoria does not usually show any further course, because it often exists from birth due to anatomical peculiarities. In those cases where it was acquired due to nervous diseases or due to diseases of the extraocular muscles, the course depends on the further development of the underlying disease.
With heterophoria, the patient usually squints. Children in particular can be affected by squinting, which often leads to bullying or teasing. The patient’s quality of life is generally reduced and everyday life becomes more difficult. It is not uncommon for the heterophoria to cause dizziness, since the patient’s vision is blurred.
The visual impairments also make daily activities more difficult and restricted. Furthermore, in many cases there are headaches or so-called double vision or blurred vision. Concentration also decreases as a result of the disease, which can have a negative effect on everyday life and school performance, especially in children. Many sufferers feel dizzy and have increased sensitivity to light.
In the treatment of heterophoria, as a rule, there are no special complications. Treatment is mainly through visual aids or surgery and does not lead to further complications. However, in most cases the surgical interventions can only be carried out in adulthood, which is why children are still dependent on visual aids.
When should you go to the doctor?
In many people, heterophoria is not pathological and does not require treatment. Up to 80% of people live with the diagnosis of heterophoria and do not notice any limitations or symptoms in everyday life. Since they describe themselves as symptom-free, no medical attention is needed in these cases. Going to the doctor is only necessary as soon as vision problems or other complaints occur. If you see double vision or blurred vision, see a doctor.
If the field of vision is perceived as blurry or unclear, it is advisable to consult a doctor. If the visual problems increase in intensity or extent over time, an eye test should be carried out immediately. If the general risk of accidents increases or if distances are misjudged, a doctor’s visit is necessary. If the usual inscriptions on traffic signs can no longer be deciphered, this is an indication of a reduction in vision that should be investigated.
If you have other symptoms such as headaches, a feeling of pressure in your head or burning eyes, these symptoms should be discussed with a doctor. If there are problems with concentration, increased irritability or if tiredness sets in prematurely despite adequate sleep at night, further examinations to clarify the cause are advisable.
Treatment & Therapy
There are basically three different forms of therapy for heterophoria that require treatment. As a passive therapy, the use of individually made glasses comes into question. The latent ametropia can be compensated in whole or in part by the spectacle lenses. This relieves the motor-sensory adjustment mechanism of the eyes so that the typical signs of fatigue do not occur and the symptoms recede quickly.
In other cases, special vision training can lead to success. It is a targeted eye muscle training, with which above all convergence training, i.e. inward movements of the eyes (near accommodation) and the avoidance of double images are trained. In addition to many other exercises, the vision training also includes visual relaxation exercises. The third form of therapy consists of a surgical intervention, which mainly affects corrections to the outer eye muscles.
The corrections are applied in such a way that the visual axes of the two eyes are as parallel as possible after the procedure in a relaxed state. This relieves the eye muscles during long-distance accommodation, so that there should be no more signs of fatigue.
Outlook & Forecast
The prognosis of heterophoria can be classified as favorable. In many cases, spontaneous remission occurs after just a few hours. The patient often does not experience any discomfort. Despite squinting, the sensory stimuli are processed correctly in the brain, so that the person concerned does not experience any impairments. The squinting is perceived by bystanders, although the affected person does not experience any significant changes in vision during the moments.
Often, a full recovery is already given with an adequate night’s sleep. Due to overexertion or fatigue, the eye is no longer able to present a full functionality. After a restful sleep, the disruptive factors are regenerated and full performance is restored.
If the heterophoria was triggered by heavy alcohol consumption, complete recovery is linked to the process of breaking down the pollutants from the organism. Consequential damage to the eye or a permanent impairment of vision is not to be expected in the case of heterophoria. Rather, the process of squinting is seen as a sign from the body that it is overwhelmed. It occurs in almost everyone at some point in life and is not considered to be of any concern. If the heterophoria occurs more frequently, the triggering cause should still be examined more closely, since there is usually a fundamental need for action.
Direct preventive measures that could prevent the development of heterophoria do not exist. The disease develops immediately after birth due to slight genetic abnormalities or is acquired through specific neuronal or muscular diseases. This means that only indirect preventive measures are conceivable that minimize the risk of a corresponding muscle or nerve disease.
In the case of heterophoria, those affected are primarily dependent on a quick and, above all, early diagnosis, since this is the only way to prevent further complications or a further deterioration of the symptoms. Self-healing is also not possible, so that treatment must be carried out in any case. Further aftercare measures are usually not available to those affected.
Parents in particular must recognize the disease in their children at an early stage and then consult a doctor immediately. In most cases, the symptoms of heterophoria are relieved relatively well by wearing glasses. Those affected must wear their glasses or contact lenses permanently so that the ametropia does not worsen.
Regular examinations and checks by an ophthalmologist are also very useful. In some cases, however, an operation is necessary. After such a procedure, the affected person needs to rest and take care of his body. Here, exertion or physical activity should be avoided in order not to unnecessarily strain the body. As a rule, the life expectancy of the affected person is not reduced by the heterophoria.
You can do that yourself
Heterophoria does not always require medical treatment. In the case of slight squinting, targeted eye muscle training is often sufficient. This special vision training is instructed by a specialist doctor and can be continued independently at home. In addition, visual relaxation exercises are used, such as visual meditation or similar measures.
If squinting causes symptoms such as headaches or dizziness, it usually helps to close your eyes for a few minutes. If the symptoms are severe, herbal remedies can be used. Headaches can be relieved with essential oils, for example. Mineral clay can also reduce throbbing while preventing dizziness. In case of lack of concentration, a lot of water should be drunk. A proven alternative from homeopathy is the remedy Belladonna, which can be taken in consultation with a naturopath.
However, if the symptoms increase, heterophoria must be treated surgically. Then the best self-help measure is to rest the affected eye after the procedure. According to the doctor’s instructions, special care products can be used to relax the irritated eye and prevent infection. If signs of inflammation become noticeable, the responsible ophthalmologist must be informed.